KR101898004B1 - Sliding Element, in Particular a Piston Ring, Having a Coating - Google Patents

Abstract

The present invention is directed to a method of manufacturing a semiconductor device having a coating comprising at least one surface comprising an adhesive layer (10), a metal containing DLC layer (12), and a nitrogen-doped non- For example, it relates to a sliding element such as a piston ring, characterized in that the nitrogen content is partitioned in the metal-free DLC layer.

Description

[0001] The present invention relates to a sliding element and a piston ring,

The invention relates to a sliding element, in particular a piston ring, which comprises a coating on at least one running surface.

For example, sliding elements such as piston rings, piston or cylinder liners of internal combustion engines should be operated over a long service life with as low friction and low wear as possible. The friction directly connected to fuel consumption in the internal combustion engine can be kept low by a diamond-like carbon (DLC) coating. Also, layer thicknesses of up to 40 micrometers can be achieved in principle. However, having a layer thickness exceeding 5 micrometers has the problem that, for example, the layer properties change in terms of the structure and composition of the layer, and therefore the required lifetime is not achieved. This applies similarly to layer thicknesses less than 5 micrometers.

In this regard, PVD coatings based on rigid materials, including mostly chromium nitride, are known. Such layers have the necessary abrasion resistance, but nevertheless do not have the required low coefficient of friction.

A sliding element comprising a DLC coating showing excellent run-in behavior is disclosed in DE 10 2005 063 123 B3. However, overall, the durability of the low coefficient of friction can be further improved.

DE 10 2008 016 864 relates to a sliding element with a coating comprising an adhesive layer, a metal-containing DLC layer and a metal-free DLC layer from the inside to the outside.

DE 197 35 962 A1 discloses a guide bush in which a rigid carbon film of hydrogenated amorphous carbon is formed on the inner surface by a plasma CVD process and a method of forming a rigid carbon film on the inner surface of the guide bush have.

Finally, WO 2006/125683 A1 discloses, from the inside outwards, a layer comprising a Group IVB, VB or VIB group element, an intermediate layer comprising a diamond-like nanocomposite composition, and a DLC layer A piston having a piston.

Although not yet disclosed, the applicant's DE 10 2009 028 504 relates to a sliding element corresponding to the premise of claim 1 of the present application.

With respect to these prior arts, the present invention aims to provide a sliding device that is further improved in terms of the combination of friction coefficient and wear characteristics.

This object is achieved by the sliding element according to claim 1.

According to claim 1, the sliding element has on at least one side a coating comprising an adhesive layer, a DLC layer containing a metal, in particular tungsten, and a metal-free DLC layer, from the inside to the outside. This coating can be provided on at least one running surface in particular. However, it is also possible to coat at least one side (flank) with its replacement or supplementation. The adhesive layer is preferably a chromium adhesive layer. The metal-containing DLC layer may contain amorphous carbon and may be set to a-C: H: M, preferably a tungsten-containing DLC layer, and a-C: H: W. The outermost or top layer also contains amorphous carbon and may be set to a-C: H. Particularly desirable properties in terms of friction and wear have been determined with the stated values. These tribological properties can affect the longer lifetime by the thicker top layer. However, if this top layer is too thick compared to the intermediate layer, the high residual stress of the layer will reduce the adhesion force, thus degrading the wear values, which may lead to delamination.

With respect to the doping of the metal-free DLC layer, it could be determined especially for the use of nitrogen so that the residual stress of the layer is preferably reduced. To be able to ensure a long lifetime of the layer, the metal-free DLC layer is doped with nitrogen, especially as soon as the critical layer thickness is reached. By this means, as mentioned above, the residual stress can be reduced and thus a higher layer thickness can be formed. Initial tests performed in the stress test produced good results. For more information on nitrogen doping and the benefits that can be achieved thereby, see Journal of Physics, vol. 30, No. 3, D.F. in Sao Paulo 2000. The article "Plasma-deposited a-C (N): H films" by Franceschini is incorporated into the main content of the present application.

While the coating is formed on at least one portion of the at least one driving surface of the sliding element, the coating may extend over the entire driving surface and may be particularly worn on the surfaces adjacent to the driving surface, e.g., the sides of the piston ring and / May be wholly or partially formed at the transition from the surface to its adjacent surfaces.

Moreover, the fractionated nitrogen content in the metal-free DLC layer Nitrogen content is now expected to additionally ensure a good path of residual stress.

Preferred examples of sliding elements according to the present invention are described in the remaining claims.

Cast iron or steel is presently preferred as a base material for sliding elements, especially piston rings. Particularly good properties could be determined for these materials.

In view of the hardness of the layer, a value of 1400 HV 0.02 to 2900 HV 0.02 is preferred for a metal-free (aC: H, upper) DLC layer and / or a value of 800 to 1600 HV 0.02 is preferred for metal (AC: H: Me) DLC layer, because the requirements in layer adhesion and cohesion are satisfactorily satisfied at these values.

Both metal-containing and metal-free DLC layers can contain hydrogen, which has proved advantageous through testing.

Moreover, the tungsten-containing DLC layer preferably comprises nanocrystalline tungsten carbide precipitates, which is beneficial in terms of physical properties.

The thickness of the adhesive layer, particularly the chromium adhesive layer, is preferably at most 1 micrometer.

A total coating thickness of from 5 to 40 micrometers, especially about 10 to 20 micrometers, is preferred so that the balance between the coefficient of friction and the wear characteristics can be met in a particularly satisfactory manner.

In view of the efficient implementation of the coating, it is presently preferred that the adhesive layer be formed by metal vapor deposition.

Advantageous manufacture of the coatings according to the invention is further ensured in terms of metal-containing and / or metal-free DLC layers, if these layers are realized by PVD and / or PA-CVD process means. In particular, the two processes mentioned above can be combined for the individual layers or two or more layers of the coating according to the invention. For nitrogen doping, in addition to carbon resulting from the ionization of acetylene in the plasma, nitrogen is essentially added as a gas during the process so that nitrogen is deposited and the layer is doped as previously described. A detailed description of the process can be found in J. Robertson's article "Diamond-like amorphous carbon" in Material Science and Engineering R 37 (2002), pages 129-281.

The thickness ratio of the metal-free DLC layer to the metal-containing DLC layer is preferably 0.7 to 1.5, and the thickness ratio of the metal-free DLC layer to the entire coating is 0.4 to 0.6. Particularly good wear values can be obtained when the intermediate layer and the top layer have approximately the same thickness, so that a ratio of thickness of approximately 1.0, in particular 0.9-1.1, or a thickness ratio of the top layer to the total layer is approximately 0.5, , And 0.45 to 0.55. The metal-containing DLC layer accounts for approximately 40 to 70% of the total layer, and the metal-free DLC layer has a thickness of approximately 4.4 to 7.6 micrometers, for example, a total thickness of 10 to 20 micrometers, Particularly preferred.

In terms of friction, it has been possible to satisfy the damage occurring in the internal combustion engine and to set a particularly constant friction coefficient, especially for the above range of coatings. Conversely, when out of the range, high friction coefficient peaks and non-uniform friction characteristics were set after a short period of time.

As a description of this behavior, although the invention is not limited in this respect, at present, the metal-free DLC layer is first introduced into the overall system, i.e. the entire coating, and the layer of the metal- containing DLC layer In the case of thickness, it is believed that very high residual stresses can be compensated in such a way that the coating is optimally realized for the combination between strength and toughness. Therefore, the sliding element coated with this, especially the piston ring, has excellent abrasion resistance. If the ratio of the layer thickness between the metal-free and metal-containing DLC layers is < 0.7 and / or the thickness ratio of the top layer to the total layer is < 0.4, then the outermost layer of the non- metal DLC layer has high abrasion resistance, The lifetime of the sliding element is very short because it does not have a thickness. Conversely, if the layer thickness ratio between the metal-free and metal containing DLC layers is > 1.5 and / or the layer thickness ratio between the top layer and the total layer is > 0.6, then the thickness of the metal- containing DLC layer is not sufficient to compensate for the residual stress . This results in premature wear of the DLC layer as a whole, despite the large thickness of the outermost layer, or a flaking-off of the DLC layer as a result of an excessively high load during operation. If the layer thickness of the metal-free a-C: H layer is further increased, this may be possible by nitrogen doping means, because the residual stress is reduced by such means and the coating process is more stable due to the improved conductivity of the top layer. Moreover, the reduction of the residual stress leads to improved friction behavior.

In addition, the nitrogen content of greater than 5 at% and / or at most 40 at% has been demonstrated to be successful in initial tests. In particular, 10 at% to 25 at% is preferred at this point in time.

Preferably, the outer portion of the metal-free DLC layer may be doped with nitrogen.

For a thickness region described as a doping region in the metal-free DLC layer, a thickness of 10 to 90% of the non-doped region is preferred. Initial tests yielded excellent results for these figures.

As described above, the sliding element according to the present invention provides a combined physical property of improved friction coefficient and wear characteristics.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described in detail below with reference to the drawings.
The drawings schematically show the structure of a coating according to one embodiment of the present invention.

As schematically depicted in the figure, a coating according to the present invention comprises, on a substrate 8, an adhesive layer 10, a metal-containing DLC layer 12, and a top layer 14, which is a metal-free DLC layer, , 16). In the example shown, the outer region 16 is doped with nitrogen and the inner region 14 is not doped with nitrogen. In the example shown, the nitrogen concentration at the doping site is approximately 15% and is only slightly partitioned in the transition from the doping site to the undoped site. In other words, the nitrogen content falls to zero in a relatively small thickness range. However, this progress can fortunately be compartmentalized.

Example

The properties of the coatings according to the invention were checked as follows. The test was carried out with two piston rings, one doped with the top layer of the coating on the drive side and one undoped.

A coefficient of friction of about 20% was measured for the doped. This can be explained by the fact that the concentration of sp2-hybridized carbon atoms increases by nitrogen doping. The sp2-hybridized carbon atoms have a graphite-like crystal structure, which makes it possible for individual crystal faces to slip in one spatial direction in the case of shear stress, and that the mechanical energy is absorbed . This results in lower friction than a layer system with lower sp2 content. It should be noted that the abrasion resistance is reduced by the sp2 content and therefore the sp2 content should not be set too high.

Those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Claims (16)

1. A sliding element having on at least one side a coating comprising an adhesive layer (10), a metal-containing DLC layer (12), and a metal-free DLC layer (14, 16)
The metal-free DLC layers 14 and 16 include at least a portion of a nitrogen-free metal-free DLC layer 16 and a nitrogen-free metal-free DLC layer 14,
The nitrogen content in the metal-free DLC layer is graduated,
Wherein the sliding element is a piston ring,
The at least a portion of the nitrogen-doped metal-free DLC layer (16) is doped with an outer region,
The doping concentration of nitrogen varies steeply in the boundary region between the nitrogen-doped non-metal DLC layer 16 and the nitrogen-undoped non-metal DLC layer 14 at least in part . The sliding element according to claim 1, wherein the sliding element comprises cast iron or steel as a base material. 3. The method according to claim 1 or 2,
The metal-free DLC layer has a hardness of 1400 HV 0.02 to 2900 HV 0.02, or
Wherein the metal-containing DLC layer has a hardness of 800 to 1600 HV0.02 or
Wherein the metal-free DLC layer has a hardness of 1400 HV 0.02 to 2900 HV 0.02 and the metal-containing DLC layer has a hardness of 800 to 1600 HV 0.02. The method according to claim 1,
Wherein at least one of the metal-containing DLC layer and the metal-free DLC layer contains hydrogen. The method according to claim 1,
Wherein the metal-containing DLC layer is a tungsten-containing DLC layer comprising nanocrystalline tungsten carbide precipitates. The method according to claim 1,
Wherein the adhesive layer has a thickness of at most 1 micrometer. The method according to claim 1,
Wherein the total coating thickness is between 5 micrometers and 40 micrometers. The method according to claim 1,
Wherein the adhesive layer is formed by metal vapor deposition. The method according to claim 1,
Wherein at least one of the metal-containing DLC layer and the metal-free DLC layer is formed by PVD process means, or PA-CVD process means or PVD process means and PA-CVD process means. The method according to claim 1,
The thickness of the metal-free DLC layer relative to the thickness of the metal-containing DLC layer has a ratio of 0.7 to 1.5,
The thickness of the metal-free DLC layer relative to the total coating thickness has a ratio of 0.4 to 0.6,
Wherein the thickness of the metal-free DLC layer is in the range of 0.7 to 1.5 with respect to the thickness of the metal-containing DLC layer, and the thickness of the metal-free DLC layer is 0.4 to 0.6 with respect to the total coating thickness. The method according to claim 1,
Wherein the metal-free DLC layer has a nitrogen content of greater than 5 at% and a maximum of 40 at%. delete The method according to claim 1,
Wherein the thickness of the doped region of the metal-free DLC layer is 10 to 90% of the thickness of the non-doped region of the metal-free DLC layer. delete The method according to claim 1,
Wherein the adhesive layer is a chromium adhesive layer having a thickness of at most 1 micrometer. The method according to claim 1,
Wherein the metal-free DLC layer has a nitrogen content between 10 at% and 25 at%.

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